Dynamics of Pluto's Atmosphere

Pluto provides an exceptional natural laboratory to study atmospheric dynamics. It is an intermediate case between fast rotators like Earth and Mars and slow rotators like Venus and Titan. It is also uniquely characterized by a near-surface stratosphere, long radiative timescales and strong N2 condensation flows. Yet, not many observations are available. Numerical climate models are therefore used to explore the atmospheric circulation. Near the surface, local downslope katabatic winds are superimposed on the flows from the subliming ice to the condensing deposits, with a Coriolis turning of the wind. Different general circulation regimes are possible, including superrotation. However, simulations performed with surface conditions most consistent with New Horizons observations suggest that the most likely regime is a global "retrorotation" forced by the conservation of angular momentum in the condensation-sublimation flows. Tidal and gravity waves are also present, creating fluctuations in the observed density profiles and the spectacular layering in the haze.